The invention is directed to the control of the upward and or downward motion of a traveling block used in conjunction with oil well drilling derricks, work-over rigs, cranes, or similar hoisting systems.
In one embodiment, the device of this invention is a safety aid installed on a derrick to control the distance a traveling block may be raised in the derrick and thus eliminate the possibility of damaging the crown block and creating a hazard to workers below. In addition, it has been desirable, as a safety measure, to prevent undue lowering of the traveling block to protect the rig floor, and thus, provide safety to the personnel on the rig floor. The systems and devices known heretofore have been based upon sensing the position of a secondary element of the system, i.e., the traveling block wire line, as it is being wrapped onto a draw works drum. The problem with such systems is that with adjustments or changes in the line used in supporting the block, corresponding adjustments must be maintained to the position of the sensing element. The adjustment has to be done on a trial-and-error basis and requires a considerable amount of time.